This invention relates, in general, to sewing machines and more particularly to an improved system for effecting the movement and location of a workholder utilized with an automatic sewing machine.
In an automatic sewing machine, an apparatus must be provided for moving a workpiece relative to the needle and, generally, it is the workpiece which is moved. The prior art sewing machines having a workholder moving in either a linear coordinate system or a polar coordinate system have certain drawbacks. When using a linear system it may be required to provide a guide for the workholder. The additional weight of such a guide increases the weight and thus inertia of the system, thereby reducing the rate of acceleration and deceleration of the system, and thus slowing the operation of the machine. As far as inertia is concerned, a non-linear or polar coordinate system reduces the inertia effects by the fact that a portion of the system is stationary. However, the main disadvantage of a non-linear system is the unwanted curvature which results. While this curvature can be compensated by altering the positioning commands to the motors, the step-wise correction inherent in the stepping motor system makes for an undesirable jagged line.